Owners of domestic dishwashers use their machines differently. Some use them as designed and intended to be used by the manufacturer, i.e., by only scraping loose soil from the ware, while at the other extreme, some rinse most of the ware in a sink before putting it in the dishwasher. The latter practice is extremely wasteful of water and is often very wasteful of energy also, if the water used for sink-rinsing has been heated.
For greatest economy, manufacturers as well as conservation-conscious governments and energy producers recommend that partial dish loads be stored in the dishwasher until it is full, and washing be done only after the unit has been fully loaded. It is further suggested that such partial loads be scraped, the dishes located in the machine, and a "Rinse & Hold" detergentless short rinse cycle be run to remove loose soil and flush it down the drain, wherever such a short rinse cycle is provided on the machine.
Various theories of dishwasher operation are prevalent in the industry today. One theory allows all but the very largest soil particles to enter the intake of the recirculating pump and be pumped through wash arms, which necessarily are provided with large nozzle openings to pass this soil without plugging. This recirculation continually pulverizes or macerates the particulate soil, reducing it even finer, and redeposits it on the ware. The end result is a requirement to use several fresh water rinses of the ware, still risking some fine redeposited soil remaining on the surface and in crevices of the ware even after the final rinse. Some more recent units of such design have the capability of collecting some of the soil from the water and holding it in position for disposal to a drain at the end of the cycle segment in which it is collected, rather than recirculating such soil to the end of that part of the cycle.
Another dishwashing theory is to filter very fine soil from the wash solution before it can reach the recirculating pump, thus avoiding recirculation of soil and redeposit problems. This also enables use of finer nozzles in the wash arms, providing greater velocity of water pressure on the ware, although smaller nozzle openings typically mean lower volume of water recirculated. Thus what is gained in one respect is lost in another. A dishwasher operating according to this theory requires additional structure to maintain the filter free to pass sufficient water therethrough for preventing pump starvation or reduction of effectiveness of the pump in carrying out its assigned water recirculating task. This is done by providing rotating backflushing jets inside (on the downstream side of) the filter, to prevent clogging of the fine filter. While such jets are ordinarily unnecessary for those users who manually rinse the ware before placement in the dishwasher, the manufacturer must nonetheless provide for the washing of heavily soiled loads of ware which may have been scraped only lightly. Since meeting worst conditions is a design criteria to market a successful product, the backflushing jets are essential with such a fine filter system. Floating soil is continually kept suspended in the sump water under this theory, and alternately adheres to the outer surface of the filter as a result of pump suction and is pressure back-washed off the filter by the backflushing action. The backflushing has the potential of further reducing particle size, depending on the softness of the soil, increasing the possibility of filter plugging and thus the requirement for greater backflushing action.
In a third theory, the one to which the present applicant subscribes as preferred, the soil is collected from the sump water without soil recirculation through the pump. Collection is accomplished as rapidly as possible, and soil is stored for later removal to drain at the next emptying of the sump. This eliminates the soil pulverizing and redeposit problem present in the first-mentioned washing theory and avoids the second theory's necessity of continually backflushing the main pump filter in order to keep operating ettectively in conditions of heavily soiled ware. A system according to this third theory is disclosed in commonly-assigned U.S. Pat. No. 4,392,891, issued July 12, 1983 to Meyers.
Most home dishwashers are provided with several dishwashing cycles from which the operator can choose to wash a specific load of dishes. Some common examples of cycle names are HEAVY SOIL for grossly soiled, scraped-only dishes, NORMAL WASH for moderately soiled dishes (some of which may have already been pre-rinsed in a RINSE & HOLD cycle), and LIGHT SOIL where little or no particulate soil is present on the ware. Cost of the buttons and controls for providing the several cycles is relatively insignificant in terms of the cost of washing dishes during the normal ten-year life of a dishwasher. A greater cost, in terms of consumption of hot water (the most typical supply temperature being 140.degree. F. (60.degree. C.) in the U.S.) is the ever-increasing cost and waste of energy in those instances where a longer cycle is selected by the operator than what is necessary under the specific conditions of a given load of dishes. Naturally, of the three most common cycles named, a HEAVY SOIL cycle is the longest in terms of time, greatest in the consumption of water and detergent and consequently the most energy intensive. Anytime a cycle is selected which is designed for a worse condition than actually present, waste will occur. And, any time a less-than-required cycle is chosen, risk is present of inadequately washing the ware. Thus, selection of the correct cycle presents somewhat of a problem to the operator, and can either be wasteful or provide inadequate results if the correct cycle (according to the soil conditions present) is not chosen.
It is not new to seek to automate cycle selection by providing the operator with only a single WASH button and having the dishwasher automatically determine the conditions of length of time of cycle, repetition of portions of a cycle, etc. in response to soil conditions. This is the intent of U.S. Pat. No. 3,888,269. Further, this goal has been discussed in meetings of home appliance designers and considered in patents, and other publications. Designers of clothes washers have also considered a similar problem and offered solutions thereto. Exemplary of such clothes washer efforts are U.S. Pat. Nos. 3,477,258; 3,114,253 and 3,279,481. Further, in the dishwasher art, while not providing for automatic cycle selection as such, U.S. Pat. No. 3,807,418 teaches that an additional rinse can be added at the end of a complete cycle if soil particles remain in the drain line of the dishwasher at the time of the final fresh water rinse.
What has been lacking in the foregoing prior art is the capability to sense a condition of particulate soil which is truly and closely indicative of the requirements to wash a given load, regardless whether the dishes are heavily, moderately or lightly soiled. The goal has been known, and attempts have been made to accomplish it. Yet no domestic dishwasher known to be on the market is capable of accurately sensing and predicting the amount of time, detergent and water to devote to a given load of dishes, and automatically operating according to those sensed conditions. This is due in part to the difficulty in determining actual soil conditions until the particulate soil is removed from the ware, descends into the sump, and is concentrated in a location where its quantity or mass can be indicated by a sensor. It is not enough to sense turbidity as in U.S. Pat. No. 3,888,269, since detergents, soil foam, stains from coffee, etc. are all capable of providing indications of turbidity while having no relation to the true soil conditions of the sump water. Nor is it enough to sense in one small area of the sump when the soil is distributed throughout the sump. Further, it is not truly effective to sense particulate soil only at the end of the final rinse and add an extra rinse, if the dishwasher is to be operated according to the aforementioned preferred theory.
What is required, therefore, is quickly to collect or concentrate particulate soil, the greatest problem in redeposition, determine the volume of particles in the concentration near the beginning of the cycle and then control the dishwasher accordingly.